The growth of a thin film of epitaxial material on a substrate surface is an important step in the fabrication of various electronic devices.
For example, infrared imagers are constructed by processes in which CdTe crystal formed on a GaAs substrate is used as the substrate for subsequent HgCdTe and HgTe/CdTe superlattice growth. Moreover, II-VI compounds are needed for electronically addressable flat panel display devices and blue laser emitting and injection devices. For applications in the blue portion of the visible spectrum, ZnSe and ZnS have long been favored candidates.
In addition, a new class of materials called diluted magnetic semiconductors (DMS) have currently received considerable attention. DMS are II-VI semiconductors such as CdTe or ZnSe with a fraction of the Group II element replaced by a magnetic transition element such as manganese. The incorporation of manganese leads to very large magnetooptic effects, on the order of several hundred times those exhibited by conventional semiconductors of a comparable bandgap.
Vapor phase epitaxy (VPE) and molecular beam epitaxy (MBE) are two techniques well known in the art for crystal growth of thin film materials. In VPE, the substrate to be coated is exposed to a vapor containing the metals to be deposited. In MBE, the substrate surface is deposited with a directed beam of molecules that contain the metals.
Photolytically or thermally decomposable metalorganic compounds have been used as the metal sources, or precursors, of the thin film material in both VPE and MBE methods. In metalorganic VPE and MBE, as the compounds are deposited on the substrate, the metals in the precursors are freed from the organic constituents, either by thermal dissociation or by photolysis or both, and combine to form an epitaxial thin film material.
Metalorganic VPE has the disadvantage that it tends to waste the rather expensive metalorganic compounds; only a small fraction of the relatively large amount of metalorganic precursors that have to be introduced into a VPE system is deposited on the substrate. MBE systems are much more efficient than VPE systems in that regard, but the amount of molecules that actually "stick" to the substrate surface still tends to be only a small percentage of the molecules that strike it.
In both metalorganic VPE and MBE, a patterned thin film of epitaxial material can be deposited onto a substrate surface by selected photolysis of the metalorganic compounds. Employment of laser irradiation to induce photolysis has greatly improved the resolution of patterned deposition, but such resolution still has been limited so far.